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위상배열 초음파를 이용한 내부 균열 및 미세 결함 검사
배시연(Siyeon Bae),정찬서(Chanseo Jeong),임병수(Byeongsoo Lim) 한국자동차공학회 2003 한국자동차공학회 춘 추계 학술대회 논문집 Vol.- No.-
The cavity nucleation, growth and coalescence are very important factors in analyzing creep characteristics. In the uniaxial creep tests, the size of cavity increased with increasing strain when stress and temperature were changed. In the case of creep crack growth, the size and number of cavities changed with the nucleation and coalescence, and the changes in crack growth and load line displacement rate followed. This resulted in the change in da/dt vs C_t. The inner defects of P92 and P122 steels were investigated by Intelligent Phased Array Ultrasonic Inspection System. The PAULI system was found to be capable of detecting the creep crack length and crack tip defects, and confirmed ultrasonic characteristics of the cavity on crack tip.
P92강의 피로 균열 성장 속도에 미치는 산화와 주파수의 영향
배시연(Siyeon Bae),강형구(Hyounggoo Kang),윤학수(Haksu Yun),이동복(Dongbok Lee),김찬우(Chanwoo Kim),임병수(Byeongsoo Lim) 한국자동차공학회 2008 한국자동차공학회 춘 추계 학술대회 논문집 Vol.- No.-
Fatigue crack growth behavior is affected by various factors. In this study, the influence of oxidation, temperature and frequency on fatigue crack growth rate had been studied for P92 alloy steel. The test of fatigue crack growth rate was carried out at temperature ranging from 550℃ to 700℃ and frequency 20Hz and 0.1Hz using compact tension specimen. As the temperature increased or load frequency decreased, fatigue crack growth rate was increased. Isothermal oxidation test was conducted at 550, 600, 650 and 700℃ for 500 hrs respectively. The oxide scale was increased as the temperature increased. The oxide scale consisted primarily of Fe₂O₃. Finally, an investigation was conducted to find relationship between fatigue crack growth and oxidation at various frequencies and temperatures.
소형 펀치 크리프 실험변수 변환에 의한 크리프 특성 평가
김범준(Bumjoon Kim),배시연(Siyeon Bae),심언태(Untae Shim),임병수(Byeongsoo Lim) 한국자동차공학회 2007 한국자동차공학회 춘 추계 학술대회 논문집 Vol.- No.-
Generally, the conventional creep specimen is tested under uniaxial stress whereas the small punch creep specimen is under multiaxial stress. The focus of this work is to investigate the relationship between the small punch creep test data and conventional creep test data by the analysis similar to the Monkman-Grant relationship using the experimentally acquired test data. Creep behavior of 9Cr-2W ferritic steel was studied at elevated temperature. Creep tests were performed using a small punch creep tester at constant loads and a conventional creep tester at constant stress. Time to fracture and the minimum displacement rate measured during the small punch tests are related in a similar manner to the corresponding conventional creep tests. From the relation derived similar to the Monkman-Grant relation, a correlation between the displacement rate in small punch creep test and the strain rate in conventional creep test is established and creep lives were evaluated by it.
초음파를 이용한 구조물 내부의 균열 및 미소 결함 검출
임병수(Byeongsoo Lim),배시연(Siyeon Bae),정찬서(Chanseo Jeong) 한국자동차공학회 2004 한국자동차공학회 춘 추계 학술대회 논문집 Vol.- No.-
The initiation and growth of internal defects usually cause the failure of long term operated structural components at high temperature. Therefore, by investigating the internal defects of material, the integrity of the system can be maintained and the unexpected failure can be prevented. The main purpose of this study is to investigate the possibility of the application of ultrasound to the measurement and estimation of the creep damage. In this study, the phased array ultrasound and backward ultrasound were employed to detect the internal defects caused by creep. The former is suitable for the detection of defects existing deep in structure while the latter is for the defects on the surface or in shallow region. Using the newly developed P92 steel. both creep and NDE ultrasound tests were performed. The results of defect inspection were checked by microstructure examination. Reliable information on the size and position of crack were obtained and successful estimation of the amount of micro-voids and their distribution proved to be obtainable by the ultrasound inspection technique. The width of the creep degraded zone was confirmed by the width of ultrasonic signal, and the severity of degradation was confirmed by ultrasonic amplitude.
코발트기 초내열합금 FSX-414의 저주기 피로 수명 평가
허인강(Inkang Heo),윤동현(Donghyun Yoon),김재훈(Jaehoon Kim),장성용(Sungyong Chang),배시연(Siyeon Bae) 대한기계학회 2017 대한기계학회 춘추학술대회 Vol.2017 No.11
Components of gas turbines must be extremely resistant to high temperatures, high stresses, high-temperature corrosion, and erosive environments. The materials used in these environmental conditions are mainly cobalt-based superalloys. In this study, the low-cycle fatigue of the cobalt-based superalloy FSX-414 was examined. The total strain range of a gas turbine between 760 ℃ and 870 ℃ was considered as the parameter representing the actual gas turbine operation. In addition, tests were performed using a trapezoidal waveform of the total strain to reflect the operation-stop conditions of a gas turbine with frequent shutdowns. The results of the fatigue test were compared with the Coffin–Manson method and energy method. The fractured surface was analyzed using a scanning electron microscope (SEM).
코발트기 초내열합금 FSX-414의 저주기 피로수명평가
허인강(Inkang Heo),윤동현(Donghyun Yoon),김재훈(Jaehoon Kim),장성용(Sungyong Chang),배시연(Siyeon Bae) 대한기계학회 2018 大韓機械學會論文集A Vol.42 No.9
가스터빈의 부품은 높은 온도와 응력, 부식과 침식 등과 같이 극한 환경에서 사용된다. 이러한 환경에 대한 저항성을 요구하는 재료로써 초내열합금이 사용된다. 본 연구에서는 코발트기 초내열합금인 FSX-414의 저주기 피로 시험을 수행하였다. 실제 작동환경을 고려하여, 760℃와 870℃의 온도조건에서 다양한 변형률의 범위로 시험을 수행하였다. 추가로 입력 파형의 경우에는 가스터빈의 기동/정지 조건을 고려하여, 사다리꼴 파형을 선택하였다. 피로 시험의 결과는 코핀-만슨 법과 에너지 법을 이용하여 예측식과 실험 결과값을 비교하였다. 피로 파단면의 경우에는 주사식 전자 현미경을 통해 분석하였다. Components of gas turbines need to be extremely resistant to elevated temperatures and stresses, corrosion, and erosive environments. The materials used under these environmental conditions are primarily cobalt-based superalloys. In this study, the low cycle fatigue of a cobalt-based superalloy, FSX-414, was examined. The total strain ranges of a gas turbine operating between 760°C and 870°C were considered the parameters representing actual gas turbine operation. In addition, fatigue tests were performed using a trapezoidal waveform to reflect the operation and stop conditions of a gas turbine with frequent shutdowns. The fatigue test results were compared with results obtained using the Manson-Coffin method and the energy method. The fractured surface was analyzed using a scanning electron microscope(SEM).